This present application relates to interior cooling channels and configurations of the blades in gas turbine engines. More specifically, but not by way of limitation, the present application relates to interior cooling channels and structural configurations formed near the outer radial tip of turbine rotor blades.
It will be appreciated that combustion or gas turbine engines (“gas turbines”) include compressor and turbine sections in which rows of blades are axially stacked in stages. Each stage includes a row of circumferentially-spaced stator blades, which are fixed, and a row of rotor blades, which rotate about a central turbine axis or shaft. In operation, generally, the compressor rotor blades rotate about the shaft, and, acting in concert with the stator blades, compress a flow of air. The supply of compressed air then is used in a combustor to combust a supply of fuel. The resulting flow of hot expanding gases from the combustion, i.e., the working fluid, is expanded through the turbine section of the engine. The flow of working fluid through the turbine is redirected by the stator blades onto the rotor blades so to induce rotation. The rotor blades are connected to a central shaft such that the rotation of the rotor blades rotates the shaft. In this manner, the energy contained in the fuel is converted into the mechanical energy of the rotating shaft, which, for example, may be used to rotate the rotor blades of the compressor, such that the supply of compressed air needed for combustion is produced, and the coils of a generator, such that electrical power is generated. During operation, because of the extreme temperatures of the hot-gas path, the velocity of the working fluid, and the rotational velocity of the engine, the blades within the turbine become highly stressed with extreme mechanical and thermal loads.
The engineering of efficient and cost-effective gas turbines is an ongoing and significant objective. While several strategies for increasing the efficiency of gas turbines are known, it remains a challenging objective because such alternatives—which, for example, include increasing the size of the engine, increasing the temperatures through the hot-gas path, and increasing the rotational velocities of the rotor blades—generally place additional strain on blades and other hot-gas path components parts that are already highly stressed. As a result, improved apparatus, methods or systems that reduce operational stresses placed on turbine blades or allow the turbine blades to better withstand these stresses so that the engines may operate more efficiently remain a significant area for technological improvement.
One strategy for alleviating the stresses on the blades is through actively cooling them during operation. Such cooling may allow the blades to better withstand higher firing temperatures and mechanical stresses, which may extend the life of the blades and generally make the engine more cost-effective and efficient to operate. One way to cool blades during operation is through the use of internal cooling channels or circuits. Generally, this involves passing a relatively cool supply of compressed air derived from the compressor through internal cooling channels. For a number of reasons, as will be appreciated, great care is required in designing and manufacturing these interior cooling channels.
First, the use of cooling air decreases the efficiency of the engine. Specifically, air from the compressor that is diverted for cooling purposes is air that otherwise could be used in the combustion process. As a result, the usage of such air necessarily decreases the air available for combustion and, thereby, decreases overall efficiency. This mandates that cooling channels be highly efficient so that air usage for cooling is minimized. Second, newer turbine blade design calls for aggressively shaped, aerodynamic configurations, which are thinner and more curved or twisted. These new blade configurations place a further premium on compact and efficient channels. These new designs also create spatial constraints that hinder or constrain the manufacture of traditional cooling channel configurations using conventional approaches. Third, interior cooling channels must be configured to promote light-weight rotor blades while still providing robust enough structure for withstanding extreme loading. That is to say, while cooling channel design is an effective way to reduce the overall weight of the blade—which promotes efficiency and reduces mechanical loads—the blades must still remain very resilient. Cooling channels, therefore, must be designed to both remove material and weight while still promoting structural resilience. Internal arrangements must also avoid stress concentrations or inadequately cooled regions (or “hot spots”) that may negatively impact part-life. Fourth, cooling configurations must also be designed so that discharged coolant promotes surface cooling and efficient, aerodynamic operation. Specifically, because cooling channels typically discharged coolant into the working fluid flowpath after circulating through the internal cooling channels, another design consideration concerns the use of discharged coolant for surface cooling as well as minimizing the aerodynamic loses associated therewith. The ejected coolant is often counted on to provide cooling to outer surfaces or regions of the blade after its release, and this must both dovetail with internal cooling strategies and take into account aerodynamic performance.
As will be appreciated, according to these and other criteria, the design of internal cooling configurations within turbine blades includes many complex, often competing considerations. Novel designs that balance these in a manner that optimizes or enhances one or more desired performance criteria—while still adequately promoting structural robustness, part-life longevity, cost-effective engine operation, and the efficient usage of coolant—represent significant technological advances.